1. Field of the Invention
The present invention relates to a disk storage apparatus in which an arbitrary sector in an alternate area provided on a disk is allocated as an alternate sector, and more particularly to a disk storage apparatus used to record AV (Audio Visual) data, and also to a retry method employed therein upon occurrence of a sector error.
2. Description of the Related Art
At present, there is a tendency to raise the storage capacity of a disk storage apparatus such as a hard disk drive (hereinafter referred to simply as an “HDD”). Accordingly, HDDs have now come to be used as AV HDDs. AV HDDs are used to record AV data, such as digital music data, digital video data, etc.
In AV HDDs, it is regarded as important to process AV data in real time. To this end, AV HDDs have a function for automatically substituting, for a normal sector, a defective sector, if it exists on, for example, a magnetic disk. This function enables continuous use of AV HDDs without reducing the access rate, even if there is a defective sector.
As is known, a disklike magnetic medium, i.e., a magnetic disk, is used as a recording medium in HDDs. It is desirable that magnetic disks should have no defects. However, in general, it is considered unavoidable, in light of manufacturing processes, that magnetic disks have several defects. Defects on magnetic disks are classified into two types. The first type of defect (defective sectors) are detected by examination executed before HDDs are shipped. The defective sectors are then substituted by normal sectors. The second type of defect (defective sectors) occurs after HDDs are shipped, during actual use by a user.
Concerning the first type of defect, the degree, number, etc. of defects can be detected. The occurrence of problems can be avoided by stopping the shipping of products if the detection result requires it. However, the second type of defect occurs at random while users are using HDDs. Accordingly, it is a matter of course that an alternate process must be executed upon detection of a second type defect. Further, there is a demand for shortening the time required for this process.
HDDs have, until recently, mostly been used as external storages for computers. Therefore, the accuracy of data stored in HDDs is very important. In the disk drive described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-255403, a sufficient restoration time is provided to enable a retry operation to be executed on an error (sector error) during reading/writing of data in a data sector. In this disk drive, restoration of the error is attempted during the restoration time. Only if the error sector is not restored is it subjected to an alternate process.
Some recent HDDs automatically allocate a normal sector in place of a defective sector, i.e., automatically execute an alternate process. For the verification of the defective sector, a lot of time is used, since, as stated above, HDDs have been used as external storages for computers. Specifically, in conventional HDDs, retry (error retry) is executed not more than a predetermined number of times on a sector that may be defective. In error retry, data is read or written from or to a sector that may be defective. Only if the error sector is not restored even after error retry is executed a predetermined number of times is the sector considered a defective one and subjected to an alternate process. Thus, in the process executed upon detection of a sector error in conventional HDDs, much more time is required for verification of a defective sector, i.e., for error retry, than for an alternate process.
As described above, in conventional HDDs, a process in which verification of a defective sector is regarded as important is executed in light of the fact that HDDs have been used as external storages for computers. Therefore, a lot of time is required for error retry executed on a sector that may be defective. This means that, in conventional HDDs, even when retry has succeeded, it is difficult to realize realtime processing of AV data. In other words, conventional HDDs are not appropriate as AV HDDs.
Furthermore, in the conventional HDDs, there is a case where the sector, in which an error has once occurred, is temporarily restored after error retry is executed thereon for a long time. In this case, the sector is not subjected to an alternate process. However, if conventional HDDs are used as AV HDDs, the time that can be used for processing a sector error is limited, and hence it is possible that an error will occur in the temporarily restored sector.